Maintaining satellite coverage of certain areas, such as the Polar Regions, for communications or surveillance is extremely difficult. Geostationary (or near-geostationary) satellites provide good persistent coverage of large areas, but are constrained to coverage latitudes below about 60° North or South. Above 60° N, ground terminals have a low elevation angle to the satellite, increasing signal attenuation from the atmosphere, geographic features, vegetation, etc.
Systems intended for complete global coverage rely on upwards of thirty or more separate spacecraft in spaced orbits and are therefore considerably complex and expensive. Sun-synchronous orbits cross the poles, but with a very short dwell time (a few minutes), and would require similarly high numbers of satellites for continuous polar coverage. Molniya or Tundra orbits are often used for long term high latitude coverage, but they are only stable at 63.4 degrees inclination, and are thus limited to direct coverage below 63.4 degrees. An otherwise identical orbit inclined at 90 degrees would start out with apogee directly over the North (or South) Pole, but its line of apsides would gradually rotate such that very little time on orbit would be spent over the pole. Conventional chemical or electric propulsion methods would not be practical for maintaining such highly-inclined eccentric orbits.